Gusseted bags have become very popular in the packaging industry. They are used extensively in the packaging of frozen foods as well as for coffee and cereal bags. Gusseted bags allow for expansion and can hold bulkier contents as compared to common pillow bags. However, this type of bag is notoriously difficult to seal. One difficulty lies in sealing across the multiple variations of layers that are unavoidable in creating a gusset.
The ends of a gusseted bag have several areas of folded material which forms the gussets. There may be areas with four layers of material on the outer edges, areas with two layers of material inboard thereof, and another area with four layers of material in the center of the gusset, resulting in a 4-2-4-2-4 layer end. While these folds are important to form the gussets, they create leak points at the transitions between the different areas of thickness.
By comparison, a pillow bag has relative uniformity with only two layers across a majority of the seal. In a pillow bag, a small four layer section resulting from the back fin seal is an insignificant percentage of the total cross seal. Pillow bags can be easily sealed using a variety of sealing technologies.
Heat has traditionally been the preferred technology for gusseted cross seals. While creating a hermetic seal is unreliable with heat, the strength of the seal is good due to its wide width. Typical heat seal jaws produce cross seals that hold approximately 8″ Hg to 10″ Hg vacuum before leaking on a common coffee pouch.
Custom contour tapered cross seal anvils have been tried with heat, offering an improvement in seal quality. The idea of the contour is to accommodate the 4-2-4-2-4 layer variation of a gusseted bag by incorporating a corresponding height variation into the seal jaws. One company that specializes in this type of sealing tools reports sealing coffee bags with contoured cross seal anvil design produced seals holds an average of 16.1″ Hg before leaks occurred. One problem with the contoured/bowed anvil approach, however, is that the taper must be gradual and the location of the gussets and fins drifts from bag to bag in production. Further, there is occasionally a two layer section on the extreme outer edges of the seal that occurs if the gussets do not line up perfectly. Since the tools are contoured away from one another at this point, a leak in this location is almost certain.
The cross sealing of gusseted bags had been attempted with ultrasonics in the past without success. A hermetic seal could be created with ultrasonics using a traditional single seal bead, but it resulted in a fragile bond that was unable to withstand real-world abuse. When the seal experienced flexing or bulging from the internal product or a vacuum burst test, the transition point where four layers meets two layers would become highly stressed and the seal would quickly fail. Quite often, the film would burst at this transition point, tearing through all layers instead of just creating a small leak path. This transition point failure had been an insurmountable hurdle for ultrasonic sealing of gussets.
U.S. Pat. No. 10,046,874, entitled “Sealing System and Method for Gusseted And Zippered Bags” (which is commonly owned with the present application), is directed to a sealing system and method that remedied many of these issues with respect to the cross seals of gusseted and zippered bags of the type described. Specifically, disclosed therein is an ultrasonic sealing tool including an anvil with a sealing surface and a horn with a sealing surface facing the sealing surface of the anvil. The sealing surface of the anvil has a plurality of beads including a first bead having a first height and at least one second bead having a second height, the second height being less than the first height. The ultrasonic sealing tool delivers ultrasonic vibrations via at least one of the anvil and the horn to create a closure seal in a work piece positioned between the anvil and the horn, the closure seal including a first seal created by the first bead and at least one second seal created by the at least one second bead, the first seal having a weld depth greater than a weld depth of the at least one second seal.
In this way, the system and method of U.S. Pat. No. 10,046,874 provides a seal of extreme depth creating a barrier on the outer edge of the bag and one or more additional seals of less depth inboard of the barrier seal to improve package strength and integrity. Since a hermetic seal of relatively low strength can be made with ultrasonics by using extreme compression, the approach of U.S. Pat. No. 10,046,874 is to add a feature or features that improves upon the strength. By adding a secondary and possibly tertiary seal of reduced weld depth, the over-compressed barrier seal can still provide the air-tight properties that are needed while the inboard, reduced depth seals keep the package from bulging and failing at the transition points. These inboard, product-side seals secure the bag and protect the barrier seal from the stress of product or vacuum test. U.S. Pat. No. 10,046,874 is hereby incorporated by reference herein in its entirety.
While the system and method of U.S. Pat. No. 10,046,874 provides greatly improved cross seals, as compared to previously known systems and methods, issues remain with respect to the manufacture of gusseted and zippered bags in some situations.
Referring to FIG. 1, the anatomy of a typical gusseted and zippered bag (10) (also referred to as a standup pouch) is shown. As is known, the bag (10) includes a gusset (12) at the bottom and a top seal (14) along the top edge. Toward the top edge is positioned a zipper (16), with one or more tear notches (18) being positioned between the zipper (16) and the top seal (14) to facilitate removal of the top seal (14) when access to the product is desired. Side seals (20) extend along both side edges of the bag (10) from the gusset (12) to the top seal (14), with there being a transition point (22), toward the gusseted end of the bag (10) transitioning from four layers of film—used to form the gusset (12) and the side seals (20)—to two layers of film—used to form the side seals (20).
The current standard for standup pouches uses premade pouches requiring a middleman (called a converter) that makes the empty pouches on relatively expensive equipment that takes up a significant amount of floor space. The pouches are then shipped to the packer where the product is inserted, and the pouch is sealed on the top thereof using an entirely different (also relatively expensive) machine. The pouches made using this method are generally attractive and have effective seals but are costly due to the extra steps required.
The packaging world has seen a growing trend toward making standup pouches on vertical form fill and seal (VFFS) equipment instead of using the premade pouches. Pouching on VFFS machinery would eliminate the converter (middleman) and the shipping costs associated with it. It would also eliminate the need for large horizontal machines, as VFFS machinery takes up a fraction of the floor space. The problem is that the side seals on pouches made on vertical machines have heretofore been generally unreliable and unattractive. In fact, the industry generally refers to these pouches as “the poor man's standup pouch.”
As discussed above, it has been found that the system and method disclosed in U.S. Pat. No. 10,046,874 provides excellent pouch side seals, particularly, along the bottom of the pouch which contains the gusset. However, it has also been found that that same system and method may not provide optimum results on the zipper end (top) of the pouch when used to try to create the side seals. Specifically, the thickness of the zipper may cause a high power draw due to melting excessive plastic on the top of the pouch. Further the system and method disclosed in U.S. Pat. No. 10,046,874 has a tendency to over-crush the zipper and scar the plastic film.
It is therefore desired to address these problems and to provide an improved seal and method of sealing particularly well suited to create the entire length of side seals on gusseted and zippered pouches.